Re: [PATCH] RDMA/rxe: Reject unknown opcodes before ICRC processing

Re: [PATCH] RDMA/rxe: Reject unknown opcodes before ICRC processing

[Leon Romanovsky]

On Mon, Apr 13, 2026 at 10:23:55PM -0700, Zhu Yanjun wrote:
> 
> 在 2026/4/13 18:17, Michael Bommarito 写道:
> > Even after applying commit 7244491dab34 ("RDMA/rxe: Validate pad and ICRC
> > before payload_size() in rxe_rcv"), a single unauthenticated UDP packet
> > can still trigger panic.  That patch handled payload_size() underflow
> > only for valid opcodes with short packets, not for packets carrying an
> > unknown opcode.  The unknown-opcode OOB read described below
> > predates that commit and reaches back to the initial Soft RoCE driver.
> > 
> > The check added there reads
> > 
> >      pkt->paylen < header_size(pkt) + bth_pad(pkt) + RXE_ICRC_SIZE
> > 
> > where header_size(pkt) expands to rxe_opcode[pkt->opcode].length.  The
> > rxe_opcode[] array has 256 entries but is only populated for defined IB
> > opcodes; any other entry (for example opcode 0xff) is zero-initialized,
> > so length == 0 and the check degenerates to
> > 
> >      pkt->paylen < 0 + bth_pad(pkt) + RXE_ICRC_SIZE
> > 
> > which does not constrain pkt->paylen enough.  rxe_icrc_hdr() then
> > computes
> > 
> >      rxe_opcode[pkt->opcode].length - RXE_BTH_BYTES
> > 
> > which underflows when length == 0 and passes a huge value to
> > rxe_crc32(), causing an out-of-bounds read of the skb payload.
> > 
> > Reproduced on v7.0-rc7 with that fix applied, QEMU/KVM with
> > CONFIG_RDMA_RXE=y and CONFIG_KASAN=y, after
> > 
> >      rdma link add rxe0 type rxe netdev eth0
> > 
> > A single 48-byte UDP packet to port 4791 with BTH opcode=0xff and
> > QPN=IB_MULTICAST_QPN triggers:
> > 
> >      BUG: KASAN: slab-out-of-bounds in crc32_le+0x115/0x170
> >      Read of size 1 at addr ...
> >      The buggy address is located 0 bytes to the right of
> >       allocated 704-byte region
> >      Call Trace:
> >       crc32_le+0x115/0x170
> >       rxe_icrc_hdr.isra.0+0x226/0x300
> >       rxe_icrc_check+0x13f/0x3a0
> >       rxe_rcv+0x6e1/0x16e0
> >       rxe_udp_encap_recv+0x20a/0x320
> >       udp_queue_rcv_one_skb+0x7ed/0x12c0
> > 
> > Subsequent packets with the same shape fault on unmapped memory and
> > panic the kernel.  The trigger requires only module load and
> > "rdma link add"; no QP, no connection, and no authentication.
> > 
> > Fix this by rejecting packets whose opcode has no rxe_opcode[] entry,
> > detected via the zero mask, before any length arithmetic runs.
> > 
> > Fixes: 8700e3e7c485 ("Soft RoCE driver")
> > Cc:stable@vger.kernel.org
> > Assisted-by: Claude:claude-opus-4-6
> > Signed-off-by: Michael Bommarito<michael.bommarito@gmail.com>
> > ---
> >   drivers/infiniband/sw/rxe/rxe_recv.c | 9 +++++++++
> >   1 file changed, 9 insertions(+)
> > 
> > diff --git a/drivers/infiniband/sw/rxe/rxe_recv.c b/drivers/infiniband/sw/rxe/rxe_recv.c
> > index f79214738c2b..413e1e954ce0 100644
> > --- a/drivers/infiniband/sw/rxe/rxe_recv.c
> > +++ b/drivers/infiniband/sw/rxe/rxe_recv.c
> > @@ -330,6 +330,15 @@ void rxe_rcv(struct sk_buff *skb)
> >   	pkt->qp = NULL;
> >   	pkt->mask |= rxe_opcode[pkt->opcode].mask;
> > +	/*
> > +	 * Unknown opcodes have a zeroed rxe_opcode[] entry (mask == 0 and
> > +	 * length == 0).  Reject them before any length math: rxe_icrc_hdr()
> > +	 * would otherwise compute length - RXE_BTH_BYTES and pass the
> > +	 * underflowed value to rxe_crc32(), producing an out-of-bounds read.
> > +	 */
> > +	if (unlikely(rxe_opcode[pkt->opcode].mask == 0))
> 
> Add rdma maillist.
> 
> if (unlikely(!rxe_opcode[pkt->opcode].mask &&
> !rxe_opcode[pkt->opcode].length))
> 
> I am not sure if "rxe_opcode[pkt->opcode].length == 0" should also be taken
> into account.
> 
> Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>

We need patch to be sent to the ML, so we can merge it.

Thanks

> 
> Zhu Yanjun
> 
> > +		goto drop;
> > +
> >   	if (unlikely(pkt->paylen < header_size(pkt) + bth_pad(pkt) +
> >   		       RXE_ICRC_SIZE))
> >   		goto drop;
> 
> -- 
> Best Regards,
> Yanjun.Zhu